Rare Plant Eats Toxic Heavy Metals in Phytoremediation Miracle

Scientists from the University of the Philippines, Los Banos, and the University of Melbourne have discovered a new species of plant that is able to absorb nickel from the soil at concentrations up to 1,000 times higher than most other plants, as reported in the journal PhytoKeys. The researchers hope that the plant might be used as a tool to help remediate contaminated soils.

The new species was identified as part of a project funded by the Department of Science and Technology -- Philippine Council for Industry, Energy, and Emerging Technology Research and Development (DOST-PCIEERD).

Species thrives in marginal soil

The new species, dubbed Rinorea niccolifera, was identified in the western region of Luzon Island in the Philippines. The soils in this area are well-known for being high in heavy metals, an environmental condition that is hostile to most species of plant. Yet, the newly discovered plant is able not only to grow in such conditions but also to thrive. The plant actively pulls nickel out of the soil, accumulating it in its tissues up to a concentration of 18,000 parts per million -- 100 to 1,000 times higher than the maximum concentrations tolerated by most plants.

Nickel hyperaccumulation such as that observed in R. niccolifera is so rare that only 450 plant species have been identified that are capable of it, out of an estimated 300,000 extant species of vascular plant worldwide. Even among plants found in nickel-rich soils, only 0.5 percent to 1 percent are capable of hyperaccumulation.

"[Hyperaccumulator] plants have great potentials for the development of green technologies, for example, 'phytoremediation' and 'phytomining,'" researcher Augustine Doronila said.

The potential of bioremediation

Phytomining refers to the use of hyperaccumulator plants to pull metals out of the soil, followed by the retrieval of those metals for commercial purposes. Phytoremediation is a more general term that refers to using plants to remove toxic agents of all varieties from the environment (and is itself a plant-specific version of the more general term bioremediation).

Because plants have adapted to so many different environments, numerous phytoremediation techniques have been discovered in addition to hyperaccumulation. Some species of plant are able to break chemical pollutants into less toxic or nontoxic components, while others absorb contaminants and expel them in a less toxic, gaseous state. Others change chemical or metallic contaminants into forms that are less easily absorbed by animal life, or bind them into the soil. Other plants stimulate the activity of soil microbes that themselves perform the actual bioremediation.

In an era of increasing soil and water contamination, bioremediation is a growing field of research. One such study, the findings of which were announced by Norwegian researchers in March, examined the conditions that might encourage naturally occurring ocean bacteria to digest oil spills more rapidly.

Many species of bacteria are able to break apart petrochemicals, but typically do so slowly, probably because such chemicals were very rare for most of evolutionary history. In the new study, researchers found that, by increasing nutrient concentration, water temperature and oxygen concentration, and reducing the influx of new water (which would naturally occur due to tides), the petroleum-digesting activity of bacteria significantly increased.

"We already knew that the bacteria would reproduce -- and thus be more effective in their work -- if they were provided with additional nutrients," researcher Roman Netzer said. "In nature, bacteria flourish best in the presence of high concentrations of phosphates and nitrogen."

The researchers hope to develop special bacterial capsules that can be attached to shorelines near oil spills.

"These will provide the bacteria with ideal growing conditions by releasing nutrients as and when needed," Netzer said.